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To get an idea of how the scale is loading the soundboard you have to consider unison tensions. All of the tension of the individual string are added together. When I’m analyzing a scale I look at a variety of things. These include the overall tension of the scale (This is the number most often used to impress non-piano folks. The Steinway D I mentioned has a total of 45,700 lbs., the Knabe 37,850 lbs., the difference being mainly in the low tenor and bass.), the unison totals for each section, graphs of unison tension, string impedance and inharmonicity, backscale lengths, and rows and rows of numbers. All of this must then be considered in reference to the soundboard design, whether the original is being used or a new board is being installed. It is also considered in reference to how the original piano sounds—assuming the piano is in good enough condition to tell.

It is rare to find an original scale with anything like a straight line anywhere in the scale. Most are quite erratic starting fairly low in the treble, rising through peaks and valleys to top out somewhere toward the mid-tenor then dropping precipitously toward the bass/tenor break. The bass is usually equally varied, often with no discernable method to the pattern.

Of the two pianos I mentioned the Knabe actually has the more uniform scale through the tenor and treble sections. The bridge has a more uniform sweep and the scale uses half-sizes throughout. It does, however, take a huge drop from G#-36 (188 x 3 = 564 lbs.) down to G#-24 (144 x 2 = 288 lbs.). The original bass/tenor break was fairly smooth by itself, but the voice characteristic from G#-36 to G#-24 changed dramatically. None of the aggressive hammer voicing techniques evidenced in the hammers had helped. Tension then levels out some before heading back down with the mono-chords, ending up with 188 lbs. at A-1. From C-88 down to G#-36 the average unison tensions in the Knabe are very close to those of the Steinway D.

With the use of new tenor and bass bridges the scale tensions of the Knabe are being brought down to 155 -165 lb. range and the bass is being brought up to better blend with the tenor scaling. The overall tension load will be 37,260 lbs., just a bit lower than the original but with much better balance. The soundboard assembly is being designed accordingly.

Like BDB, I cringe when I hear manufacturers (not just Knabe) bragging about using original scales in some resurrected piano. We can do better and the piano buyer deserves better.

The last Knabe (5'-8") I restrung I did not bother to note the original scale, since I am aware of their deficiencies. But although Knabe did use half-sizes in the low tenor, I found that I could get a smoother scale using whole sizes. If there is an extreme foreshortening of the scale, sometimes you have to skip a half-size there, or even more. I aim for a low deviation, and in the case of this Knabe, it was less than 4 lb. The top of the scale, about the last 2 octaves, are all strung with the same size wire, showing that the designer aimed for the theoretic geometric curve in the bridge, and then screwed it all up by changing gauges.

Originally posted by BDB: The last Knabe (5'-8") I restrung I did not bother to note the original scale, since I am aware of their deficiencies. But although Knabe did use half-sizes in the low tenor, I found that I could get a smoother scale using whole sizes. If there is an extreme foreshortening of the scale, sometimes you have to skip a half-size there, or even more. I aim for a low deviation, and in the case of this Knabe, it was less than 4 lb. The top of the scale, about the last 2 octaves, are all strung with the same size wire, showing that the designer aimed for the theoretic geometric curve in the bridge, and then screwed it all up by changing gauges. [/b]

That piano is a whole other kettle of fish or something. This piano switches to bi-chord wrapped strings fairly high up in the tenor. The new scale will be switching ever further up and they will be placed on a transition bridge.

Your point about whole wire size changes is well taken, but it really applies only to the lowest part of the tenor bridge and then only when the bridge has been foreshortened a fair amount. The rest of the scale is generally better off using half-sizes.

Originally posted by Jan-Erik: Do not the force on the bridges vary, independently of the string tension, but because of height of bridge?

I thougt this was teh main issue with low or high strung pianos. But this is perhaps a different topic. [/b]

They are interdependent.

If you replace a set of strings with higher tensions (i.e., larger diameters) on a given piano and make no other changes the string deflection angle across the bridge will be less than it was originally. The more taut string would require more force from the soundboard/bridge assembly to deflect it the same amount.

Originally posted by grandpianoman: Del, it sounds to me after reading your posts, that the original string scales can be improved upon? I believe that is what will happen with the new set of bass strings I will be getting for my RBB.

Thanks again for your excellent posts.

Gpman [/b]

Yes, almost always. My only warning would be to have the scaling done by someone who knows what they are doing. You want someone who is more cautious than brave. The idea is to even things out and correct for obvious scaling flaws, not try to make it into a whole other piano.

Unless, of course, you are trying to make it into a whole other piano. Then it is always safe to decrease string tensions -- rarely is it safe to increase them. For example, I am reducing the tensions through the tenor of the little Knabe I've been talking about, since the plate was obviously strong enough to hold the original higher tension scale this will be perfectly safe. (I'm also designing a new soundboard to work with the reduced scale tensions.) I would never increase the tensions on, say, a Steinway S, M, L, O or A. These plates were designed to work with relatively low-tension scales and I would not want to over stress them with a higher tension scale.

Thanks Del, I belive that is exactly what will be done with my bass strings...his calculations actually follow pretty close to the original scale, but he sees the areas where he can improve in order to smooth out the breaks etc. He is definitely not going the route of changing the scale to make a "new" piano.

Interesting, I always heard that Steinway was a high tension piano..

Before doing all this research on bass strings and reading your posts, I did not realize how complicated and important stringing a piano can be. It can alter the sound quite a bit.

Your point about whole wire size changes is well taken, but it really applies only to the lowest part of the tenor bridge and then only when the bridge has been foreshortened a fair amount. The rest of the scale is generally better off using half-sizes.

Half-sizes may be better lower in the tenor, but without adding more hitch pins, one must take an average. The point is that to get a better scale, you usually have to change gauges more often the lower in the scale.

This is a comparison of the before (top) and after tensions on the last piano that I restrung. The lowest notes, on the left of the graphs, are the highest wound strings. The first pair of plain strings are 2 full sizes heavier than the next pair. But it still should be evident which should be the more even scale. (The peak at note 87 is probably just the result of a slight inaccuracy in the measurement of the speaking length.)

Not exactly, because it would be comparing old strings with new ones. Still, there are some trends. The biggest difference is less of a fall-off of volume as you approach the break. There are some pianos that have a great deal of inharmonicity near the break, and scaling this way improves that problem greatly. They are much easier to tune. Some scales have problem areas which clear up. Of course, with more uniform tension, the piano stays in tune better.

I suspect that problems with what people characterize as the "killer octave" may be the result of bad scaling in that area. As you can see in the top graph, the tension was extremely high in that area, meaning the strings were very thick for their length. That cannot be good.

This piano has the original soundboard and bridge, about 80 years old. The work was done on-site, eliminating moving costs. The question of the effect of soundboard design on sound is much more difficult. Rescaling takes just a couple of hours to measure the speaking length and stare at the numbers to come up with something reasonable. That is cheap enough to do even for a small improvement. Replacing the soundboard would double the cost of restoration with no guarantee that there will be a significant improvement. That makes no sense.

Thanks BDB, very interesting......one of the big decisions I had to make was whether or not to keep the original, already repaired soundboard and bridges. In the end, we kept it, because it had excellent sustain, good crown, and the piano sounded very good as it was....one of those cases where it made no sense to replace it since it was functioning properly.

The fellow I received the original scale from said one of the important factors was to get the core wire diameter correct, and that seems to be part of what your saying here as well, in order to get a good and even sounding scale.

No, I have not delved into bass string design. Again, too many factors to be certain of the results. For the most part, the bass string manufacturers know their business fairly well, often better than the piano designers.

Originally posted by BDB:...I suspect that problems with what people characterize as the "killer octave" may be the result of bad scaling in that area. As you can see in the top graph, the tension was extremely high in that area, meaning the strings were very thick for their length. That cannot be good.

This piano has the original soundboard and bridge, about 80 years old. The work was done on-site, eliminating moving costs. The question of the effect of soundboard design on sound is much more difficult. Rescaling takes just a couple of hours to measure the speaking length and stare at the numbers to come up with something reasonable. That is cheap enough to do even for a small improvement. Replacing the soundboard would double the cost of restoration with no guarantee that there will be a significant improvement. That makes no sense. [/b]

While many pianos do, indeed have relatively poor scaling through the fifth and sixth octaves, many more do not. The abnormally percussive attack coupled with a too rapid drop-off is a soundboard issue. It is not something that can be solved by either scaling or hammer voicing.

Soundboard replacement—when necessary—does solve the problem and the results are quite predictable. Assuming the shop doing the replacement knows what it is doing, of course.

Originally posted by BDB: No, I have not delved into bass string design. Again, too many factors to be certain of the results. For the most part, the bass string manufacturers know their business fairly well, often better than the piano designers. [/b]

Most string winders, such as Mapes, follow factory specifications pretty closely. They will custom wrap, but they clearly don’t want to. Others, GC Strings in Canada among them, wrap to their own specifications which may or may not follow factory specifications. If you order from them you get what they want to wrap with little say in the matter.

There are several other string winders — Jim Arledge is one of them — who can help with bass string scaling if this is not something you want to do. As well, there are several rebuilders who offer string scale calculation as part of their business.

Bass string scaling is not all that difficult to learn and many improvements can be made here. Essentially is it a question of working out the ratio between core wire diameters and overall loading to achieve a desired balance in between string tensions, string impedance and inharmonicity.

Soundboard replacement—when necessary—does solve the problem and the results are quite predictable. Assuming the shop doing the replacement knows what it is doing, of course.

I suspect that almost everyone who replaces soundboards knows nothing about the design of them, and just replaces with a copy of the original. How many people do you think there are in the world who could do otherwise? (And do they agree on the solution?)

I suspect that they follow industry standards. However, factory specifications are not likely to be available for enough pianos that they would have to be able to design strings on their own very quickly.

I have a Steinway O ( or some other piano), do I need to measure the piano to order replacement strings? Easily the most commonly asked question, and the answer is yes. In a perfect world, the same model of piano from the same manufacturer would have the same measurements. However, even the finest piano models vary from piano to piano with regard to speaking length. This variance is enough to drastically effect the sound quality if the wrong measurements are used. To get the best possible sound, we design and manufacture our strings using measurements taken from YOUR piano, not someone else's. (A fine example would be the Mason & Hamlin AA, which varies by as much as 1.5 centimeters in the bass speaking lengths, even for the same model year.)

Why rescale my piano? If your piano has been rebuilt it has already been inadvertently rescaled. Present methods of string duplication make it virtually impossible to get strings remade to the manufacturer's original specification. We rescale to our original aural and mathematical standards to give you an optimum set of new bass strings.

Was my scale perfect? The original scale was done by trial and error prior to the days of computer enhancement. Depending on the manufacturer and model, the amount of attention to scale design varied greatly. Some old scales are in fact virtually perfect, but most can be improved.

Can a computer generate a perfect scale? While the beauty of a scale is determined by ear, duplication of that beauty can be translated from piano to piano by today's formulations. We can define the parameters of good piano sound, the proper mixture of tension and inharmonicity, thus finding each note's "sweet spot".

Does good sound have a mathematical component? Superb piano sound, mathematically speaking, is a balance between string tension and inharmonicity. Mathematics helps us arrive at the optimum values for each of these by helping us choose the ideal core wire size (inharmonicity), and the ideal copper build-up (tension). Both of these values are calculated to match the note's speaking length.

What about the bare lengths? The bare lengths (the core wire in the speaking section which has no copper) are a critical factor in the string's inharmonicity. Typically, with each replacement set of bass strings, a string winder will increase these bare lengths as a "margin of safety". By a second rebuild, the string winders hay have added over an inch of unwanted bare length to each string at both ends. They do this to insure that your new strings will fit, unaware of the disastrous effect on the piano's inharmonicity.

What about the different sizes of wire and wrap? It is essential for the best results in string design that the string winder have all of the size options for both copper and steel wire. Few string winders have all of the size options for both copper and steel wire. We do! If the string winder does not have all of the sizes, then he must redesign and substitute. Is this the right way to get the best job possible?

Will rescaling solve my tonal problems? Properly scaled and accurately constructed strings will sound great! Learn to ask, "Do these strings have a pleasant sound?" After all, what else should be the ultimate test? If a bass string does not pass this test, even on a light blow, then something is wrong with that string and it should be replaced. That's the only cure. We guarantee our strings will sound great.

Soundboard replacement—when necessary—does solve the problem and the results are quite predictable. Assuming the shop doing the replacement knows what it is doing, of course.

I suspect that almost everyone who replaces soundboards knows nothing about the design of them, and just replaces with a copy of the original. How many people do you think there are in the world who could do otherwise? (And do they agree on the solution?)

I suspect that they follow industry standards. However, factory specifications are not likely to be available for enough pianos that they would have to be able to design strings on their own very quickly. [/b]

I have no idea how many rebuilding shops there are world-wide that are competent enough to replace soundboards. I expect there are probably fifty or so in the U.S. And, as pianos continue to age, the number is growing. You might check out the upcoming PTG Conference in Rochester, NY which will have quite an emphasis on soundboard technology.

Mapes has the original bass string scaling for a vast number of U.S. built (and quite a few imported) pianos. If they don’t have the original scale they fake it by using one that is similar. At least that has been their past practice. It may have changed in the past several years. We purchase all of our steel wire from them but we no longer use their bass strings.

Originally posted by Jan-Erik: The soundboard is the soul the piano (Vincent Chavanne). I have heard that the result soundboard replacement is very hard to predict. [/b]

So I've heard.

When I started to investigate the soundboard and its function one of the first things I was told was that soundboard performance was difficult to predict. And now one really knew why. This was almost regarded as the holy grail of the piano business. The more I learned, however, the more I found that only certain types of soundboard systems are unpredictable; those that are purely compression-crowned. That is, those that depend entirely on the internal, perpendicular-to-grain expansion and compression of the wood grain to form and hold crown. Others, specifically those that depend on curved ribs for their crown, are both more predictable and longer-lived.

There are rebuilding shops using both methods. Those using compression-crowning techniques maintain tight controls over their process and produce work that is at least as consistent as that of the manufacturers still using compression-crowned soundboard systems. (At least those that I am familiar with do.) Those shops using rib-crowning techniques (and we are among them) also maintain tight control over the whole process. It is a bit easier to predict results because we do not depend quite so much on the variable qualities of wood.

I suppose if one is working with a shop that is installing its first soundboard assembly — assuming the person in charge has not bothered to take advantage of the vast amount of training and information now available — the results might be unpredictable. But, of course, the same thing could be said of a shop installing its first set of hammers or wippens. Or doing its first restringing job. Or to the tuner doing his or her first tuning or voicing job.

I was not asking about replacing soundboards per se. I was asking about people who can redesign and replace soundboards. It sounds like your shop could well be the only one in the US that can redesign a soundboard, Del.

Originally posted by BDB: I was not asking about replacing soundboards per se. I was asking about people who can redesign and replace soundboards. It sounds like your shop could well be the only one in the US that can redesign a soundboard, Del. [/b]

Ah, well...I don't really know. I'd like to think there are at least a few out there. If for no other reason than I've been teaching this stuff for a fair number of years now. I hope it's not all gone to waste.